Page 21 - MetalForming-Jan-2018-issue

slide motion throughout the stroke and tonnage generated on a workpiece. Via a servo press, metalformers can opti- mize the press cycle for different appli- cations by adjusting slide motion. The specific results of this capability have been outlined in Study of Servo Drive Press Technology—A Review, a report recently published in the International Journal of Innovative Research in Sci- ence, Engineering and Technology.
“The flexible programming of a servo drive press allows (users) to set the most suitable forming velocity for the given forming operation and mate- rial; dwell the slide anywhere in the stroke at the desired stroke position; carry out secondary operations; and provide the necessary time for part transfer,” it reads.
Instead of shaping material into forms via brute force, controlled slide motion of the servo press enables material to flow into a form. As a result, unique aspects of a particular part or forming operation can be accounted for during job programming, allowing for smooth press operation with rela- tively less stress on tooling while deliv- ering parts that can approach the tol- erances and accuracies of fineblanked parts.
The ability of such presses to dwell– at any point within the press stroke– enables the time necessary to conduct accurate and high-quality secondary operations such as tapping or fastener insertion, for example. Beyond creating a tight-tolerance part, this adds to process value without the need for costly and time-consuming off-press secondary processing.
Servo-press technology also offers other ways to positively affect part quality. Consider deep drawing. By combining servo presses with die cush- ions, blankholder force can be varied throughout the deep-drawing steps. Changing the blankholder force— matching cushion movement to the speed of the slide—enables optimum blankholder force throughout, in step with the slide motion. Thus, wrinkles and fractures can be avoided.
During blanking, servo presses can
Instead of shaping material into forms via brute force, controlled slide motion of a servo press enables material to flow into a form... allowing for smooth press operation with relatively less stress on tooling while delivering parts that can approach the tolerances and accuracies of fineblanked parts.
eliminate burrs by increasing slide speed near the point of impact. In addi- tion, because tight punch-die clear- ances reduce the likelihood of burrs, specific slide and motion programming can ensure that such clearances are maintained.
Springback, common especially in higher-strength materials, affects the dimensional accuracy of parts, and can be minimized via servo-press use. Pro- gramming variable velocity, as well as dwell or bottom-dead-center positions, helps reduce springback effects.
And, servo-press technology enables a shortened forming cycle, as a short stroke can be dialed in near bottom- dead-center, with higher slide speeds during return.
Save Your Tooling
Tool-life improvements, like so many other advantages inherent in servo presses, arise from slide-motion
control. Controlling punch velocity during forming reduces tool-wearing heat generation arising from friction, not to mention the probable increase in scrapped bad parts. And, slide motion tied to a particular application helps ensure minimal stress on die components, reducing the likelihood of tool breakage and resulting costly downtime. In general, the ability to reduce the touching speed of the tool to a workpiece will extend tool life and avoid high impact loads. In addition, optimized slide motion reduces the chances of vibrations occurring in the work material, which, again, can impact tool life and part quality.
And, servo presses, with program- mable slide motion, can form parts at lower tonnages than more static mechanical presses. This also aids tool longevity.
Part recipes with customized motions and slide velocities enable more work to be performed in fewer die stations. This can lower tool-build and -maintenance costs. As servo presses continue to become common- place, more tool designers and builders are creating dies specifically to take advantage of the technology. More and more operations can be fitted into servo-press tooling, leading to greater productivity gains while further reduc- ing the need for out-of-press secondary processes.
Getting the most out of tooling in servo-press operations—and out of the servo press itself—means optimiz- ing. Of course, experimenting and refining, which leads to optimized job programming, is a tough sell when testing must occur on the shop floor. That’s why some metalformers opt for servo presses as tryout equipment. Besides self-optimization, servo- mechanical presses can mimic the actions of traditional hydraulic and mechanical presses, making them ideal as tryout machines.
In one case, seeing the trend toward common use of servo presses, a tool- builder decided to replace an offline- for-repair 400-ton mechanical press with a 330-ton servo model. While the
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